Low bend loss optical fiber

ABSTRACT

Disclosed herein are optical waveguide fibers comprising: (I) a core comprising an outer radius r 1 , a maximum refractive index delta percent Δ 1 max  and core alpha, α, of larger than 5; and (II) a cladding surrounding the core, the cladding comprising: (i) an inner cladding region having outer radius r 2  and refractive index delta percent Δ 2 , wherein Δ 1max &gt;Δ 2 ; (ii) a trench region surrounding the inner cladding region, the trench region having an outer radius, r 3  where r 3 ≧10 microns and refractive index delta percent Δ 3 ; and (iii) an outer cladding region having chlorine concentration of ≧1.2 wt. % surrounding the trench region and comprising refractive index delta percent Δ 4 , wherein Δ 1max &gt;Δ 4  and Δ 2 &gt;Δ 3 , and Δ 4 &gt;Δ 3  and wherein the difference between Δ 4  and Δ 3  is ≧0.12 percent.

This application claims the benefit of priority under 35 U.S.C. §119 ofU.S. Provisional Application Ser. No. 62/314,607 filed on Mar. 29, 2016,the content of which is relied upon and incorporated hereby reference inits entirety.

FIELD

The present invention relates to optical fibers having low bend losses.

TECHNICAL BACKGROUND

There is a need for low bend loss optical fibers, particularly foroptical fibers utilized in so-called “access” and fiber to the premises(FTTx) optical networks. Optical fiber can be deployed in such networksin a manner which induces bend losses in optical signals transmittedthrough the optical fiber. Some applications that can impose physicaldemands, such as tight bend radii, compression of optical fiber, etc.,that induce bend losses include the deployment of optical fiber inoptical drop cable assemblies, distribution cables with FactoryInstalled Termination Systems (FITS) and slack loops, small bend radiusmultiports located in cabinets that connect feeder and distributioncables, and jumpers in Network Access Points between distribution anddrop cables.

SUMMARY

According to at least some embodiments, disclosed herein are opticalwaveguide fibers comprising: (I) a core comprising an outer radius r₁, arefractive index delta percent Δ_(1max), and core alpha, α>5; and (II) acladding surrounding the core, the cladding comprising: (i) an innercladding region having outer radius r₂ and refractive index deltapercent Δ₂, wherein Δ_(1max)>Δ₂; (ii) a trench region surrounding theinner cladding region, the trench region having an outer radius r₃ wherer₃≧10 microns, and refractive index delta percent Δ₃; and (iii) an outercladding region having chlorine concentration of ≧1.2 wt. % surroundingthe trench region and comprising refractive index delta percent Δ₄,wherein Δ_(1max)>Δ₄ and Δ₂>Δ₃, and 4₄>Δ₃ and wherein the differencebetween Δ₄ and Δ₃ is ≧0.12 percent. The fiber has a mode field diameterMFD>9 microns at a 1310 nm wavelength, cable cutoff of less than 1260nm, and bend loss at 1550 nm for a 15 mm diameter mandrel of less than0.5 dB/turn, and 1300 nm≦λ₀≦1324 nm, where 4 is the zero dispersionwavelength.

In some embodiments the profile volume, |V₃| of the trench region is atleast 30% Δmicron². In some embodiments the profile volume,|V₃| of thetrench region is at least 45%, and in some embodiments at least 50%Δmicron². According to some embodiments the core alpha is at least 10.

Fibers having a trench region (depressed index region) in the claddinghave improved (reduced) microbending losses. The trench region in thecladding may be formed either by down doping the trench region (e.g. byfluorine (F) doping or by doping with non-periodic voids) or by updopingthe outer cladding region. In other embodiments, the fibers may includeboth a trench region and an outer cladding region which is updoped withrespect to silica (SiO₂), i.e. a cladding region which includes an indexincreasing dopant such as germania (GeO₂) or chlorine (Cl) in sufficientamounts to appreciably raise the index of silica.

In some embodiments 1.2≦r₂/ r₁≦2.5, for example 1.2≦r₂/r₁≦2.35, between1.25 and 2.3, or between 1.25 and 2.15. In at least some of theexemplary embodiments described herein 1.6≦r₂/r₁≦2.4.

In some embodiments the difference between Δ₄ and Δ₃ is at least 0.15percent. In some embodiments the difference between Δ_(1max) and Δ₂ isgreater than or equal to at least 0.25 percent, the difference betweenΔ_(1max) and Δ₃ is greater than or equal to at least 0.35; and thedifference between Δ₂ and Δ₃ is greater than or equal to at least 0.08percent.

In some embodiments Δ₄ and Δ₂ have the same value. In some embodimentsthe difference between Δ₄ and Δ₂ is greater than 0.01 percent. In someembodiments, the difference between Δ₄ and Δ₃ is between 0.15 and 0.4percent, in some embodiments the difference between Δ₄ and Δ₃ is between0.15 and 0.2 percent; and in some embodiments 0.38≦Δ_(1max)−Δ₃≦0.65, forexample 0.4≦Δ_(1max)−Δ₃≦0.5. In some embodiments 0.15≦Δ_(1max)−Δ₂≦0.45;0.38≦Δ_(1max)−Δ₃≦0.6; 0.1≦Δ₂−Δ₃≦0.3; and 0.1≦Δ₄−Δ₃≦0.2. In someembodiments, 0.25≦Δ_(1max)−Δ₂≦0.35 and 0.4≦Δ_(1max)−Δ₃≦0.5 and0.14≦Δ₂−Δ₃≦0.2. In some embodiments, 0.15≦Δ₄−Δ₃≦0.2.

The fiber embodiments have optical properties that are G.652 compliant,MFD between 9.0 and 9.5 microns at 1310 nm, zero dispersion wavelength,λ₀, in the range 1300 nm≦λ₀≦1324 nm, cable cutoff less than or equal to1260 nm (e.g., between 1000 nm and 1260 nm), and attenuation at 1550nm≦0.185 dB/km, and in at least some embodiments ≦0.181 dB/km at 1550 nm(e.g., 0.17 to 0.18 dB/km).

The exemplary fibers disclosed herein are capable of exhibiting a wiremesh covered drum microbend loss (i.e., an increase in attenuation fromthe unbent state) at 1550 nm (WMCD at 1550nm) which is less than orequal to 0.07 dB/km and in some embodiments less than or equal to 0.05dB/km, such as for example 0.005 to 0.05 dB/km. The exemplary fibersdisclosed herein are capable of exhibiting a basketweave microbend lossat −60 ° C. (i.e., an increase in attenuation from the unbent state) at1550 nm which is less than or equal to 0.05 dB/km, in some embodimentsless than or equal to 0.02 dB/km, and in some embodiments less than orequal to 0.01 dB/km such as for example 0.001 to 0.01 dB/km.[0012]Additionally, the fiber embodiments disclosed herein exhibit abend loss that is not more than 0.5 dB/turn at 1550 nm when wound arounda 15 mm diameter mandrel. In other embodiments, the 15 mm diameter bendloss at 1550 nm is not more than 0.3 dB/turn, and in some embodimentsnot more than 0.2 dB/turn, or even less than 0.1 dB/turn (e.g., 0.075dB/turn to 0.29 dB/turn, or 0.09 dB/turn to 0.25 dB/turn). In someembodiments, the 30 mm diameter bend loss (fiber wound around a 30 mmdiameter mandrel) at 1550 nm is not more than 0.02 dB/turn, for examplenot greater than 0.01 dB/turn, and in some embodiments no more than0.005 dB/turn, or in some embodiments no more than 0.003 dB/turn at 1550nm.

At the same time, these fiber embodiments are capable of providing anattenuation at 1550 nm which is less than or equal to 0.185 dB/km, forexample, less than 0.182 dB/km, (e.g., 0.17 dB/km to 0.182 dB/km or 0.17dB/km to 0.18 dB/km), as well as an attenuation at 1310 nm which is lessthan or equal to 0.34 dB/km, for example not greater than 0.32 dB/km.

Such bend loss and attenuation performance numbers are attainable usinga primary and a secondary coating applied to the fiber, wherein theYoung's modulus of the primary is less than 2 MPa, in some embodimentsless than 1 MPa, and in some embodiments less than 0.5 MPa. The Young'smodulus of the secondary coating is greater than 500 MPa, more in someembodiments greater than 1000 MPa, and in some embodiments greater than1500 MPa. In some embodiments, the outer diameter of the secondarycoating is 242 microns. In some other embodiments, the outer diameter ofthe secondary coating is 200 microns.

Reference will now be made in detail to the present embodiments,examples of which are illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a refractive index profile corresponding to one embodimentof an optical waveguide fiber as disclosed herein.

FIG. 2 shows a refractive index profile to an embodiment of an opticalfiber as disclosed herein.

FIG. 3 shows a refractive index profile of an embodiment of an opticalfiber as disclosed herein.

FIG. 4 shows a refractive index profile of an embodiment of an opticalfiber as disclosed herein.

FIG. 5 shows a refractive index profile of an embodiment of an opticalfiber as disclosed herein.

FIG. 6 shows a refractive index profile of an embodiment of an opticalfiber as disclosed herein.

FIG. 7 shows a refractive index profile of an embodiment of an opticalfiber as disclosed herein.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Additional features and advantages will be set forth in the detaileddescription which follows and will be apparent to those skilled in theart from the description or recognized by practicing as described in thefollowing description together with the claims and appended drawings.

According to at least some embodiments the optical fibers have lowbend-induced losses especially for tight bends, such as 15 mm diameterbends, for applications in data centers and fiber to the homeinstallations. According to at least some embodiments the optical fibersdisclosed herein are backward compatible with existing installed fibernetwork systems. According to at least some embodiments, the opticalfibers disclosed herein have a 1310 mode filed diameter of >9 microns inorder to have low splice losses with existing installed optical fibers.Optical fibers disclosed herein can be cabled and can be part of anetwork system having a transmitter and receiver.

The “refractive index profile” is the relationship between refractiveindex or relative refractive index and the fiber radius. The radius foreach segment of the refractive index profile is given by theabbreviations r₁, r₂, r₃, r_(4a), r₄, etc. and lower an upper case areused interchangeability herein (e.g., r₁ is equivalent to R₁).

The “relative refractive index percent” (also referred to herein as“refractive index delta percent”, “relative refractive index”,“refractive index delta”, and “relative refractive index delta”) isdefined as Δ%=100×(n_(i) ²−n_(c) ²)/2n_(i) ², and as used herein n_(c)is the average refractive index of undoped silica. As used herein, therelative refractive index is represented by Δ and its values are givenin units of “%”, unless otherwise specified. The terms: delta, Δ, Δ%,%Δ, delta%, % delta and percent delta may be used interchangeablyherein. For embodiments described herein, an equivalent relativerefractive index profile can be obtained by shifting the entirerefractive index profile of the optical fiber is either up or down. Incases where the refractive index of a region is less than the averagerefractive index of undoped silica, the relative refractive indexpercent is negative and is referred to as having a depressed region ordepressed index. In cases where the refractive index of a region isgreater than the average refractive index of the cladding region, therelative refractive index percent is positive. An “updopant” is hereinconsidered to be a dopant which has a propensity to raise the refractiveindex relative to pure undoped SiO₂. A “downdopant” is herein consideredto be a dopant which has a propensity to lower the refractive indexrelative to pure undoped SiO₂. Examples of updopants include GeO₂(germania), Al₂O₃, P₂O₅, TiO₂, Cl, Br. Examples of down dopants includefluorine and boron. In some embodiments the core comprises germaniadoped silica. In some embodiments the maximum germania concentration inthe core region, [GeO₂]_(core-max), in weight percent is 4 wt. % 23[GeO₂]_(core-max)≦13 wt. %, in some embodiments 6 wt.%≦[GeO₂]_(core-max)≦12 wt. %, and in some embodiments 7 wt.%≦[GeO₂]_(core- max)≦11 wt. %. In some embodiments the core compriseschlorine doped silica. In some embodiments the maximum chlorineconcentration in the core region, [Cl]_(core-max), in weight percent is1 wt. %≦[Cl]_(core-max)≦7 wt. %, in some embodiments 1 wt.%≦[Cl]_(core-max)≦6 wt. %, and in some embodiments 1.5 wt.%≦[Cl]_(core-max)≦6 wt. %.

“Chromatic dispersion”, herein referred to as “dispersion” unlessotherwise noted, of a waveguide fiber is the sum of the materialdispersion, the waveguide dispersion, and the inter-modal dispersion. Inthe case of single mode waveguide fibers the inter-modal dispersion iszero. Zero dispersion wavelength is a wavelength at which the dispersionhas a value of zero. Dispersion slope is the rate of change ofdispersion with respect to wavelength.

“Effective area” is defined as in equation 1 as:Δ_(eff)=2π(∫f ² r dr)²/(∫f r dr)   Eq. 1where the integration limits are 0 to Go, r is the radial distance fromthe center of the core, and f is the transverse component of theelectric field associated with light propagated in the waveguide. Asused herein, “effective area” or “A_(eff)” refers to optical effectivearea at a wavelength of 1550 nm unless otherwise noted.

The term “α-profile” refers to a refractive index profile, expressed interms of Δ(r) which is in units of “%”, where r is radius, which followsthe equation 2, shown belowΔ(r)=Δ(r _(o))(1−[|r−r_(o)|/(r ₁ −r _(o))]^(α))   Eq. 2where r_(o) is the point (radial location) in the core at which Δ(r) ismaximum, r₁ is the point at which Δ(r)% is zero, and r is in the ranger_(i)≦r≦r_(f) , where Δ is defined above, r_(i) is the initial point ofthe α-profile, r_(f) is the final point of the α-profile, and α is anexponent which is a real number (referred to as “core α”, “ core alpha”,“alpha value” or “α value” herein).

The mode field diameter (MFD) is measured using the Peterman II methodwherein, 2w=MFD, and w²=(2∫f² r dr/∫[df/dr]² r dr), the integral limitsbeing 0 to ∞.

The bend resistance of a waveguide fiber can be gauged by inducedattenuation under prescribed test conditions, for example by deployingor wrapping the fiber around a mandrel of a prescribed diameter, e.g.,by wrapping 1 turn around a either a 6 mm, 10 mm, or 20 mm or similardiameter mandrel (e.g. “1×10 mm diameter macrobend loss” or the “1×20 mmdiameter macrobend loss”) and measuring the increase in attenuation perturn.

One type of bend test is the lateral load microbend test. In thisso-called “lateral load” test (LLWM), a prescribed length of waveguidefiber is placed between two flat plates. A #70 wire mesh is attached toone of the plates. A known length of waveguide fiber is sandwichedbetween the plates and a reference attenuation is measured while theplates are pressed together with a force of 30 Newtons. A 70 Newtonforce is then applied to the plates and the increase in attenuation indB/m is measured. The increase in attenuation is the lateral loadattenuation of the waveguide in dB/m at a specified wavelength(typically within the range of 1200-1700 nm, e.g., 1310 nm or 1550 nm or1625 nm).

Another type of bend test is the wire mesh covered drum microbend test(WMCD). In this test, a 400 mm diameter aluminum drum is wrapped withwire mesh. The mesh is wrapped tightly without stretching, and shouldhave no holes, dips, or damage. Wire mesh material specification:McMaster-Carr Supply Company (Cleveland, Ohio), part number 85385T106,corrosion-resistant type 304 stainless steel woven wire cloth, mesh perlinear inch: 165×165, wire diameter: 0.0019″, width opening: 0.0041″,open area %: 44.0. A prescribed length (750 meters) of waveguide fiberis wound at 1 m/s on the wire mesh drum at 0.050 centimeter take-uppitch while applying 80 (+/−1) grams tension. The ends of the prescribedlength of fiber are taped to maintain tension and there are no fibercrossovers. The attenuation of the optical fiber is measured at aspecified wavelength (typically within the range of 1200-1700 nm, e.g.,1310 nm or 1550 nm or 1625 nm); a reference attenuation is measured onthe optical fiber wound on a smooth drum. The increase in attenuation isthe wire mesh covered drum attenuation of the waveguide in dB/km at aspecified wavelength (typically within the range of 1200-1700 nm, e.g.,1310 nm or 1550 nm or 1625 nm).

Another type of bend test is the basketweave microbend loss test. In thebasketweave microbend loss test, the fibers are wound at high tension ona glass spool and exposed to a temperature cycle. The testing apparatuscomprises of a fixed diameter silica drum. The drum surface is smooth.In this test, the drum diameter is 110 mm. The fiber is wound onto theglass drum with a winding tension of 70 grams, and a pitch of 2 mm(distance between adjacent wraps of fiber). Multiple layers of fiber arewrapped with this tension and pitch. The pitch angles are reversed witheach layer wound. The crossover of the tensioned fibers from theadjacent layers creates the microbend mechanism. A fiber length of 2.5km is used. The initial fiber attenuation measurement is performed atabout 23°, at about 45% RH (relative humidity) with the fiber deployedin the basketweave configuration with 70 grams of tension. Initialattenuation loss measurements are made at wavelengths of 1310 nm, 1550nm, and 1625 nm. An OTDR (optical time domain reflectometer) is used toacquire the attenuation loss data.

After the initial attenuation loss measurement at 23° C., the fiber issubjected to thermal cycling. In the thermal cycling, the fiber is firstcooled from 23° C. to −60° C. at a rate of 1° C./min. The fiber ismaintained at 60° C. for 20 hours and then heated at a rate of 1° C./minback to 23° C. The fiber is maintained at 23° C. for 2 hours, thenheated to 70° C. at a rate of 1° C./min and maintained at 70° C. for 20hours. The fiber is then cooled to 23° C. at a rate of 1° C./min andmaintained at 23° C. for two hours. The fiber is then subjected to asecond thermal cycle, which was identical to the first thermalcycle—i.e., it is cooled from 23° C. to −60° C., then heated back to 23°C., maintained at that temperature for 2 hours and then heated from 23°C. to 70° C., after which it is cooled back to 23° C. Finally, aftermaintaining the fiber at a temperature of 23° C. for two hours, afterthe second cycle, the fiber is once again cooled to −60° C. at a rate of1° C./min, held at −60° C. for 20 hours, and then further cooled at arate of 1° C./min to 60° C. The fiber is held at −60° C. for 20 hours,then heated at a rate of 1° C./min back to 23° C. and held at 23° C. for2 hours. The thermal cycling is concluded at this point.

During the thermal cycling of the fiber, the attenuation loss of thefiber is measured continuously. The maximum attenuation loss over thetwo thermal cycles down to −60° C. is determined, and the differencebetween this maximum attenuation loss and the initial attenuation lossat 23° C. is reported herein, as the basketweave microbend loss of thefiber over the temperature range from −60° C. to 70° C. In the thermalcycle down to −60° C., the difference between the attenuation lossmeasured at −60° C. and the initial attenuation loss at 23° C. isreported herein as the basketweave microbend loss of the fiber over thetemperature range from −60° C. to 23° C.

The “pin array” bend test is used to compare relative resistance ofwaveguide fiber to bending. To perform this test, attenuation loss ismeasured for a waveguide fiber with essentially no induced bending loss.The waveguide fiber is then woven about the pin array and attenuationagain measured. The loss induced by bending is the difference betweenthe two measured attenuations. The pin array is a set of ten cylindricalpins arranged in a single row and held in a fixed vertical position on aflat surface. The pin spacing is 5 mm, center to center. The pindiameter is 0.67 mm. During testing, sufficient tension is applied tomake the waveguide fiber conform to a portion of the pin surface. Theincrease in attenuation is the pin array attenuation in dB of thewaveguide at a specified wavelength (typically within the range of1200-1700 nm, e.g., 1310 nm or 1550 nm or 1625 nm).

The theoretical fiber cutoff wavelength, or “theoretical fiber cutoff”,or “theoretical cutoff”, for a given mode, is the wavelength above whichguided light cannot propagate in that mode. A mathematical definitioncan be found in Single Mode Fiber Optics, Jeunhomme, pp. 39-44, MarcelDekker, New York, 1990 wherein the theoretical fiber cutoff is describedas the wavelength at which the mode propagation constant becomes equalto the plane wave propagation constant in the outer cladding. Thistheoretical wavelength is appropriate for an infinitely long, perfectlystraight fiber that has no diameter variations.

Fiber cutoff is measured by the standard 2m fiber cutoff test, FOTP-80(EIA-TIA-455-80), to yield the “fiber cutoff wavelength”, also known asthe “2 m fiber cutoff” or “measured cutoff”. The FOTP-80 standard testis performed to either strip out the higher order modes using acontrolled amount of bending, or to normalize the spectral response ofthe fiber to that of a multimode fiber.

By cabled cutoff wavelength, “cable cutoff”, “cable cutoff wavelength”,or “cabled cutoff” as used herein, we mean the cable cutoff wavelengthdetermined by the 22 m cabled cutoff test described in the EIA-445 FiberOptic Test Procedures, which are part of the EIA-TIA Fiber OpticsStandards, that is, the Electronics Industry Alliance—TelecommunicationsIndustry Association Fiber Optics Standards,

Unless otherwise noted herein, optical properties (such as dispersion,dispersion slope, etc.) are reported for the LP01 mode.

Optical fibers disclosed herein are capable of exhibiting an effectivearea at 1550 nm which is greater than about 70 microns², in someembodiments between 75 and 95 microns², for example between about 80 and90 microns². In some embodiments, the optical mode effective area at1550 nm is between about 82 and 88 microns².

The embodiments of the fiber 10 is (see, for example, FIG. 1) include acore 12 with comprising maximum refractive index delta percent Δ₁,and acladding 20 that surrounds the core 12. In at least some embodimentsdisclosed herein the core alpha is larger than 5 (i.e., α>5). Accordingto the exemplary embodiments described herein, fiber 10 is preferably asingle mode fiber.

The cladding 20 includes inner cladding region 21 that is in contactwith and surrounds the core 12, a depressed index cladding region 22(also referred to as a trench region herein) that surrounds the innercladding region 21. The cladding region 22 has a refractive index deltapercent Δ₃. The outer cladding region 24 surrounds the trench region 22and comprises a refractive index delta percent Δ₄. A trench region is alow refractive index region, surrounded by the higher refractive indexregions. As shown for example, in FIG. 1, the trench region 22 withinthe cladding 20 is surrounded by two higher index cladding regions-i.e., cladding regions 21 and 24.

In the embodiments described herein Δ_(1max)>Δ₄; Δ₃<Δ₂, and Δ₄>Δ₃. Inthe embodiments illustrated in FIGS. 1-7, cladding regions 21, 22 and 24are immediately adjacent one another. However, this is not required, andalternatively, additional cladding regions may be employed.

The core 12 comprises an outer radius r₁(which is defined as where atangent line drawn through maximum slope of the refractive index deltapercent of central core 12 crosses the zero delta line) that is between2.75 and 6 microns, in some embodiments between about 3 and 5.75microns, for example between 3.5 and 5.6 microns, and in someembodiments 4-5 microns. Core 12 exhibits a refractive index deltapercent Δ₁, (relative to pure silica). For example the maximumrefractive index delta of the core, Δ_(1max), may be 0 percent (if it ismade of pure silica) to 0.65 percent, or between 0.15 and 0.5 percent,and in some embodiments between about 0.2 and 0.5 percent. In someembodiments Δ_(1 max)≧0.38, for example 0.5≧Δ_(1max)≧0.38.

In some embodiments, the core 12 exhibits a core alpha (α) wherein, a isgreater than 5, for example at least 10. In some embodiments the corealpha is 15 or greater. In some embodiments, the core 12 may comprise analpha between about 10 and 100, for example in some embodiments the corealpha, a, may be between 15 and 100, and in some embodiments between 15and 40. A refractive index profile of an exemplary fiber embodiment withα₁ of about 20 is shown, for example, in FIG. 1.

In the embodiments illustrated in FIGS. 3-7, the inner cladding region21) is adjacent to the core 12 and comprises inner radius r₁ and outerradius r₂. The inner cladding region 21 preferably exhibits a refractiveindex delta percent, Δ₂≦0.3 (relative to pure silica). As stated above,Δ₁≧Δ₂. In the exemplary embodiments described herein,0.15%≦Δ_(1max)−Δ₂≦0.5%, for example 0.2%<Δ_(1max)−Δ₂<0.4%, or0.25%<Δ_(1max)−Δ₂≦0.35. In some embodiments Δ₂ is 0 to 0.3 percent, forexample between about 0 and 0.25 percent, or between 0.1 and 0.2percent. Alternatively, for example, if the core region 12 (alsoreferred to as a core herein) is made of pure silica, the inner claddingregion 21 is downdoped relative to pure silica, such thatΔ_(1max)−Δ₂≦0.5 percent. The outer radius r₂ of the inner claddingregion 21 is between 5 and 17 microns, in some embodiments between about7 and 15 microns, for example 6 to 12 microns, or 6 to 10 microns. Insome embodiments the ratio of r₂/r₁ is >1.2. In some embodiments theratio of r₂/r₁ is ≧1.25, for example 1.25≦r₂/r₁≦2.5. In at least some ofthe exemplary embodiments described herein 1.6≦r₂/r₁≦2.4. In at leastsome of the exemplary embodiments described herein 1.8≦r₂/r₁≦2.35. Theabove values of the radius r₁, the difference between Δ_(1max) and Δ₂,and the r₂/r₁ ratio help the fibers have 1300 nm ≦λ₀≦1324 nm and MFDbetween 8.2 microns and 9.5 microns at the 1310 nm wavelength.

The trench region 22 (also referred to as depressed index claddingregion herein) surrounds the inner cladding region 21. The trench region22 has a refractive index delta percent Δ₃ that is smaller than Δ₂. Insome embodiments Δ₃ is −0.4%≦Δ₃≦0.1%. For example, in some embodimentsthe trench is formed of pure silica, and Δ₃ is 0. In some embodimentsthe relative refractive index delta percent in the trench region 22 isessentially flat, i.e. the difference between the relative refractiveindex delta percent at any two radii within the trench region 22 is lessthan 0.03%, and in some embodiments less than 0.01%. In otherembodiments there can be fluctuations as a result of small profiledesign or process variations. In some embodiments, the trench region 22comprises silica which is substantially undoped with either fluorine orgermania, i.e., such that the region is essentially free of fluorine andgermania, i.e., less than 0.1 wt. % F or GeO₂. In some embodiments, thetrench region is pure silica, in other embodiments it is silica dopedwith fluorine, in order to make −0.4%≦Δ₃≦0.1%. In some embodiments,0.35%≦Δ_(1max)Δ₃≦0.65%.

The trench region 22 preferably exhibits a width W_(t) (whereinW_(t)=r₃−r₂) between about 4 microns and 22 microns, in someembodiments, between 8 and 20 microns. In some embodiments, the outerradius r₃ of the trench region may be not less than 10 microns, forexample greater than 12 microns and less than 27 microns, or about 14.5microns to about 25.5 microns in order to achieve good bend performanceand a cable cutoff of ≦1260 nm. Outer cladding region 24 surrounds thetrench region 22 and comprises refractive index delta percent Δ₄ whichis higher than the refractive index delta percent Δ₃ of the trenchregion 22, thereby forming a region which is an “updoped” outer claddingregion 24 with respect to the depressed index cladding region 22, e.g.,by adding an amount of dopant (such as germania or chlorine) sufficientto increase the refractive index of the outer cladding region. In someembodiments, there is no fluorine or other down dopants in the trenchregion 22, and the outer cladding region 24 comprises an updopant, forexample chlorine. In some embodiments, the chlorine concentration in theouter cladding region 24 is ≧1 wt. %. In some other embodiments, thechlorine concentration in the outer cladding region 24 is ≧1.2 wt. %. Instill other embodiments, the chlorine concentration in the outercladding region 24 is ≧1.5 wt. %. In yet other embodiments, the chlorineconcentration in the outer cladding region 24 is ≧2 wt. %. Outercladding region 24 comprises a higher refractive index than that of thetrench region 22, and may, for example, have a refractive index deltapercent Δ₄ which is between 0.12% and 0.4%. In some embodiments0.12%≦Δ₄Δ₃≦0.4%, for example in some embodiments 0.12%<Δ₄−Δ₃≦0.3%. Insome embodiments, the outer cladding region 24 is comprised of a firstouter cladding region 24 a (with an outer radius r_(4a)) and a secondouter cladding region 24 b (with an outer radius r₄), wherein the firstouter cladding region 24 a has a chlorine concentration of ≧1.2 wt %from r₃ to 40 microns. In some embodiments first outer cladding region24 a has a chlorine concentration of ≧1.5 wt. % from r₃ to 40 microns,and in some embodiments, the first outer cladding region 24 a has achlorine concentration of ≧2 wt. % from r₃ to 40 microns. In someembodiments, the second outer cladding region 24 b has a higherviscosity than the first outer cladding layer. That is, the viscosity ofthe glass of the second outer cladding region 24 b is greater than theviscosity of glass of the first outer cladding region 24 a. In thisembodiment the second outer cladding region 24 b is the tensionabsorbing layer. In some embodiments, the second outer cladding region24 b has a chlorine concentration of ≦0.5 wt. % from r_(4a) to r₄ (wherer_(4a) is the outer radius of the high (e.g., ≧1.2 wt. % Cl) updopedregion, as shown for example in FIG. 2, and r₄ is the outer radius ofthe glass optical fiber, for example, 62.5 microns). In some embodimentsthe second outer cladding region 24 b has a chlorine concentration of≦0.25 wt. % from its inner radius r_(4a) to the outer radius r₄. In someembodiments the second outer cladding region has a chlorineconcentration, [Cl], of 0.0 wt. % [Cl]≦0.2 wt. % from r_(4a) to r₄. Insome embodiments, 40 microns≦r_(4a)≦55 microns, for example r_(4a) is at40 microns, 45 microns, 50 microns, or 55 microns. Preferably, thehigher index portion (compared trench region 22) of outer claddingregion 24 extends at least to the point where the optical power whichwould be transmitted through the optical fiber is greater than or equalto 90% of the optical power transmitted, more preferably to the pointwhere the optical power which would be transmitted through the opticalfiber is greater than or equal to 95% of the optical power transmitted,and most preferably to the point where the optical power which would betransmitted through the optical fiber is greater than or equal to 98% ofthe optical power transmitted, which is preferred to achieve good bendperformance and a cable cutoff of ≦1260 nm. In some embodiments, this isachieved by having the “updoped” third annular region (i.e., the firstouter cladding region 24 a) extend at least to a radial point of about30 microns. In some embodiments, the “updoped” third annular region 24 aextends at least to a radial point of about 40 microns, with a fourthannular region (i.e., the second outer cladding region 24 b) comprisingessentially of silica surrounding the third annular region. In someembodiments, the cladding 20 has an outer diameter of 2 times themaximum radius, R_(max), of about 125 micron. As shown in FIG. 2, theupdoped region 24 a (i.e., the first outer cladding region) of the outercladding 24, has a refractive index delta percent of Δ₄ and the claddingregion 24 b (i.e., the second outer cladding region) has a refractiveindex delta percent of Δ₅, and Δ₄>Δ_(5.)

The profile volume V₃ of the trench region 22, is calculated usingΔ₍₄₋₃₎(r)rdr between radius r₂ and r₃, and thus is defined in equation 3as

$\begin{matrix}{V_{3} = {2{\int\limits_{r\; 2}^{r\; 3}{{\Delta_{({4 - 3})}(r)}{rdr}}}}} & {{Eq}.\mspace{14mu} 3}\end{matrix}$

All volumes are in absolute magnitude (i.e., V₃=|V₃|). In order toachieve good bend performance, the volume V₃ of the trench region 22 ispreferably greater than 30% Δmicron², and may be greater than 45%Δmicron² , and in some embodiments is greater than 50% Δmicron², and insome embodiments may be greater than 55% Δmicron². In some embodimentsthe volume V₃ of the trench region 22 is 30% Δmicron² to 90% Δmicron²,for example 40 to 80% Δmicron².

In the exemplary embodiments disclosed herein the core 12 has a positiverefractive index throughout. The core region 12 comprises a maximumrefractive index delta percent Δ_(1max) occurring between r=0 and r=3microns. In these embodiments Δ₁ max is between about 0.38% and about0.5%.

The fibers are capable of exhibiting a bend loss of less than 0.5dB/turn when wound upon on a 15 mm diameter mandrel for fibers with MACnumbers ≧7.25. In some embodiments, the optical fibers disclosed hereinhave a MAC number of ≧7.6 or even ≧7.7 and in some examples, 7.6≦MAC≦8,and a zero dispersion wavelength, λ₀ of 1324 nm≧λ₀≧1300 nm. As usedherein, MAC number means mode field diameter at 1310 (nm) divided by 22m cable cutoff wavelength (nm).

The fibers disclosed herein may be drawn from optical fiber preformsmade using conventional manufacturing techniques and using known fiberdraw methods and apparatus, for example as is disclosed in U.S. Pat.Nos. 7,565,820, 5,410,567, 7,832,675, 6,027,062, the specifications ofwhich are hereby incorporated by reference.

Various exemplary embodiments will be further clarified by the followingexamples. It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the claims.

EXAMPLES

Table 1 below lists characteristics of fiber embodiments examples 1-3.These fiber embodiments have refractive index profiles as shown in FIGS.3-5. In particular, set forth below for each example is the refractiveindex delta percent Δ₁, alpha 1 (α1), and outer radius r₁ of the core12; refractive index delta percent Δ₂, and outer radius r₂ of the innercladding region 21; and refractive index delta percent Δ₃, and outerradius r₃, as well as profile volume V₃ of the trench region 22, whichis calculated between r₂ and r₃; refractive index delta percent Δ₄. Alsoset forth are chromatic dispersion and dispersion slope at 1310 nm,chromatic dispersion and dispersion slope at 1550 nm, mode fielddiameter at 1310 nm and 1550 nm, lateral load wire mesh microbend at1550 nm, pin array macrobend at 1550 nm, zero dispersion wavelength(Lambda 0), 22 m cable cutoff, MAC number at 1310 nm, 1×15 mm diameterbend loss (bend loss when the fiber is turned once around a 15 mmdiameter mandrel), and spectral attenuation at 1310 and 1550 nm.

TABLE 1 Parameter Ex 1 Ex 2 Ex 3 Δ1max (%) 0.47 0.47 0.45 r₁ (micron)4.3 4.3 4.3 Region12 20 20 20 Core Alpha Δ2 (%) 0.15 0.15 0.15 Δ1 − Δ20.32 0.32 0.30 r₂ (micron) 10 9 8.1 r₂/r₁ 2.3 2.1 1.9 Δ3 (%) 0.00 0.000.00 Δ2 − Δ3 0.15 0.15 0.15 r₃(micron) 20 19.5 20 Δ4 (%) 0.15 0.15 0.15r₄(micron) 62.5 62.5 62.5 Max chlorine 1.5 1.5 1.5 concentration inouter cladding region 24, weight % Δ4 − Δ3 0.15 0.15 0.15 V₃ 45 45 50 (%micron²) Dispersion at 4.9E−04 0.346 0.25 1310 nm (ps/nm/km) Dispersion0.088 0.099 0.091 Slope at 1310 nm (ps/nm²/km) Lambda 1318 1315 1315zero, nm Dispersion at 17.5 18 18 1550 nm (ps/nm/km) Dispersion 0.0620.062 0.063 at Slope 1550 nm (ps/nm{circumflex over ( )}2/km) MFD at1310 9.2 9.16 9.25 nm (micron) MFD at 1550 10.44 10.34 10.38 nm (micron)LLWM @ 0.6 0.56 0.77 1550 nm, dB/m WMCD at 0.04 0.04 0.04 1550 nm, dB/kmPin Array at 14.9 15.0 23.9 1550 nm, dB Cable Cutoff 1206 1206 1200 (nm)Aeff at 1310 66.5 65.9 67.2 nm (micron²) Aeff at 1550 85.6 84.0 84.6 nm(micron²) MAC # (MFD 7.63 7.60 7.71 at 1310 nm/Cable Cutoff) 1 × 15 mm0.19 0.2 0.29 diameter bend loss at 1550 nm (dB/turn) 1 × 20 mm 0.0470.047 0.074 diameter bend loss at 1550 nm (dB/turn) 1 × 30 mm 0.00450.0045 0.01 diameter bend loss at 1550 nm (dB/turn) Attn at 1550 ≦0.18≦0.18 ≦0.18 nm, dB/km Attn at 1310 ≦0.32 ≦0.32 ≦0.32 nm, dB/km

As can be seen in Table 1 above, the exemplary fibers shown in Table 1employ a glass core region 12 having index Δ₁, an inner cladding region21 having index Δ₂, and cladding trench region 22 having refractiveindex delta percent Δ₃, and an outer cladding region 24 havingrefractive index delta percent Δ₄; wherein Δ_(1max)>Δ₂; Δ_(1max)>Δ₄;Δ₃>Δ₂; Δ₄>Δ₃, wherein the difference between Δ_(1max) and Δ₂ is greaterthan or equal to at least 0.15, difference between Δ_(1max) and Δ₃ isgreater than or equal to at least 0.35 (e.g., 0.38≦Δ_(1max)−Δ₃≦0.65);the difference between Δ₂ and Δ₃ is greater than or equal to at least0.08 (e.g., 0.08≦Δ₂−Δ₂≦0.4); and the difference between Δ₄ and Δ₃ isgreater than or equal to at least 0.08 (e.g., 0.1≦Δ₄−Δ₃≦0.4, or0.1≦Δ₄−Δ₃≦0.3); and the absolute value of profile volume, |V₃| is atleast 30% micron². These fibers have mode field diameters (MFD) at 1310nm between 9 microns and 9.5 micron, for example between 9.2 microns and9.5 microns and a zero dispersion wavelength between 1300 nm and 1324nm. These fibers have an attenuation of ≦0.18 dB/km and ≦0.32 dB/km at1550 nm and 1310 nm, respectively.

Table 2 below lists characteristics of a fiber example 4 embodiment.This fiber embodiments has the refractive index profile as shown in FIG.6.

TABLE 2 Parameter Ex 4 Δ1max (%) 0.53 r₁ (micron) 4.4 Region12 CoreAlpha 20 Δ2 (%) 0.2 Δ1 − Δ2 0.33 r₂ (micron) 10 r₂/r₁ 2.27 Δ3 (%) 0.00Δ2 − Δ3 0.2 r₃(micron) 18.2 Δ4 (%) 0.2 r_(4a)(micron) 45 Max chlorineconcentration, in 2 outer cladding region 24, weight % Δ4 − Δ3 0.2 Δ5(%) 0 r₄(micron) 62.5 V₃ (% micron2) 46.2 Dispersion at 1310 nm 0.483(ps/nm/km) Dispersion Slope at 1310 nm 0.089 (ps/nm²/km) Lambda zero, nm1312 Dispersion at 1550 nm 18.1 (ps/nm/km) Dispersion at Slope 1550 nm0.062 (ps/nm²/km) MFD at 1310 nm (micron) 9.16 MFD at 1550 nm (micron)10.31 LLWM @ 1550 nm, dB/m 0.4 WMCD at 1550 nm, dB/km 0.04 Pin Array at1550 nm, dB 8.96 Cable Cutoff (nm) 1257 Aeff at 1310 nm (micron²) 66.1Aeff at 1550 nm (micron²) 81.7 MAC # (MFD at 1310 7.29 nm/Cable Cutoff)1 × 15 mm diameter bend loss 0.102 at 1550 nm (dB/turn) 1 × 20 mmdiameter bend loss 0.023 at 1550 nm (dB/turn) 1 × 30 mm diameter bendloss 0.002 at 1550 nm (dB/turn) Attn at 1550 nm, dB/km ≦0.18 Attn at1310 nm, dB/km ≦0.32As can be seen in Table 2 above, the exemplary fibers such as thatdepicted in FIG. 2 and FIG. 6 employ a glass core region 12 havingrefractive index delta percent Δ_(1max), an inner cladding region 21having refractive index delta percent Δ₂, and trench region 22 havingrefractive index delta percent Δ₃, and an first outer cladding region 24a having refractive index delta percent Δ₄ and a second outer claddingregion 24 b having a refractive index delta percent Δ₅; whereinΔ_(1max)>Δ₂; Δ_(1max)>Δ₄; Δ₃>Δ₂; Δ₄>Δ₃, wherein the difference betweenΔ_(1max) and Δ₂ is greater than or equal to at least 0.15, differencebetween Δ_(1max) and Δ₃ is greater than or equal to at least 0.35 (e.g.,0.38 ≦Δ_(lmax)−Δ₃≦0.65); the difference between Δ₂ and Δ₃ is greaterthan or equal to at least 0.08 (e.g., 0.08≦Δ₂−Δ₂≦0.4); and thedifference between Δ₄ and Δ₃ is greater than or equal to at least 0.08(e.g., 0.1≦Δ₄−Δ₃≦0.4, or 0.1≦Δ₄−Δ₃≦0.3); and an absolute value ofprofile volume, |V₃| of at least 30% micron². In this embodiment, thecladding region 24 b is a silica layer with a relative refractive indexpercent of about zero. The cladding region 24 b (i.e., the second outercladding region) acts as a stiff tension absorbing layer. This fiberembodiment has a mode field diameter (MFD) at 1310 nm between 9 micronsand 9.5 micron, and a zero dispersion wavelength between 1300 nm and1324 nm.

The fiber embodiments described herein exhibit a cable cutoff less thanor equal to 1260 nm and a bend loss of less than 0.5 dB/turn when woundupon on a 15 mm diameter mandrel. These fibers also exhibit a mode fielddiameter between about 9 and 9.5 microns at 1310 nm, a zero dispersionwavelength between 1300 and 1324 nm, a dispersion slope at 1310 nm whichis less than or equal to 0.092 ps/nm²/km. These fibers exhibit a WireMesh Covered Drum (WMCD) bend loss at 1550 nm which is less than orequal to 0.07 dB/km, in some embodiments less than or equal to 0.06dB/km, and in some embodiments less than or equal to 0.05 dB/km. Thesefibers also exhibit a pin array bend loss at 1550 nm which is less than8.5 dB, in some embodiments less than 5 dB and in some embodiments lessthan 4 dB. These fibers exhibit a Basketweave microbend loss at 1550 nmwhich is less than or equal to 0.05 dB/km, in some embodiments less thanor equal to 0.025 dB/km, and in some embodiments less than or equal to0.01 dB/km.

Many of these fibers also exhibit a bend loss at 1550 nm, when woundupon on a 15 mm diameter mandrel, of less than 0.5 dB/turn, and in somecases less than 0.2 dB/turn. These fibers also exhibit a bend loss at1550 nm, when wound upon on a 20 mm diameter mandrel, of less than 0.2dB/turn, in some embodiments less than 0.15 dB/turn, and some fibers insome embodiments less than 0.1 dB/turn. These fibers also exhibit a bendloss at 1550 nm, when wound upon on a 30 mm diameter mandrel, of lessthan 0.02 dB/turn, for example less than 0.005 dB/turn, or even lessthan 0.003 dB/turn.

Such bend loss and attenuation performance numbers are attainable usinga primary and secondary coating applied to the fiber, wherein theYoung's modulus of the primary is less than 2 MPa, in some embodimentsless than 1 MPa, and in some embodiments less than 0.5 MPa. The Young'smodulus of the secondary coating is greater than 500 MPa, in someembodiments greater than 1000 MPa, and in some embodiments greater than1500 MPa. In some embodiments, the outer diameter of the secondarycoating is 242 microns. In some other embodiments, the outer diameter ofthe secondary coating is 200 microns.

Table 3 provides data of a manufactured optical fiber embodiment(Example 5 fiber). The refractive index profile of optical fiber example5 fiber is illustrated in FIG. 7.

TABLE 3 Data for manufactured optical fiber Parameter Ex 5 Δ_(1max) (%)0.48 r₁ (microns) 4.87 Core Alpha, α 20 r₂ (microns) 6.11 r₂/r₁ 1.25 Δ₂(%) 0.153 R₃ (microns) 19.8 Δ₃ (%) 0 V₃(% Δ micron²) 60 Δ₄ (%) 0.168Chlorine conc, in outer 1.7 cladding region 24, weight % r₄ (microns)62.5 Dispersion at 1310 nm 0.565 (ps/nm/km) Dispersion Slope at 1310 nm0.091 (ps/nm²/km) Dispersion at 1550 nm 18.1 (ps/nm/km) Zero DispersionWavelength (nm) 1304 MFD at 1310 nm (microns) 9.34 MFD at 1550 nm(microns) 10.45 Aeff at 1550 nm (micron²) 85.8 Cable Cutoff (nm) 1204Macrobend Loss for 15 mm 0.078 mandrel diameter at 1550 nm (dB/turn)Macrobend Loss for 20 mm 0.084 mandrel diameter at 1550 nm (dB/turn)Macrobend Loss for 30 mm 0.005 mandrel diameter at 1550 nm (dB/turn)Microbend loss at 1550 nm in 0.005 Basket-weave test at −60 C. for 242microns coating diameter (dB/km) Microbend loss at 1550 nm in 0.03Basket-weave test at −60 C. for 200 microns coating diameter (dB/km)Microbend loss at 1550 nm in 0.03 Basket-weave test at −60 C. for 200microns coating diameter (dB/km)

In the embodiment of Table 3, the optical fibers exhibits a basketweavemicrobend loss at −60° C. at 1550 nm which is less than or equal to 0.05dB/km, for example less than or equal to 0.03 dB/km.

In some embodiments, the fiber core may comprise a relative refractiveindex profile having a so-called centerline dip which may occur as aresult of one or more optical fiber manufacturing techniques. However,the centerline dip in any of the refractive index profiles disclosedherein is optional.

The optical fiber disclosed herein comprises a core 12 and a cladding 20surrounding and directly adjacent to the core. According to someembodiments, the core is comprised of silica doped with germanium, i.e.germania doped silica. According to some embodiments, the core iscomprised of silica doped with chlorine, i.e., chlorine doped silica.Dopants other than germanium or chlorine, singly or in combination, maybe employed within the core, and particularly at or near the centerline,of the optical fiber disclosed herein to obtain the desired refractiveindex and density. In embodiments, the core region 12 of the opticalfiber 10 disclosed herein has a non-negative refractive index profile,more preferably a positive refractive index profile, with the innercladding region 21 surrounding and directly adjacent to core region 12.

The optical fiber disclosed herein may be surrounded by a protectivecoating, e.g. a primary coating P contacting and surrounding the outercladding region 24, the primary coating P having a Young's modulus ofless than 1.0 MPa, in some embodiments, less than 0.9 MPa, and in someembodiments not more than 0.8 MPa, and further comprises a secondarycoating S contacting and surrounding the primary coating P, thesecondary coating S having a Young's modulus of greater than 1200 MPa,and in some embodiments greater than 1400 MPa.

According to some embodiments, with primary and secondary coatings, theouter diameter of the secondary coating is less than 250 microns.According to some embodiments the fiber further is coated with primaryand secondary coatings, and the outer diameter of the secondary coatingis less than 210 microns.

As used herein, the Young's modulus, elongation to break, and tensilestrength of a cured polymeric material of a primary coating is measuredusing a tensile testing instrument (e.g., a Sintech MTS Tensile Tester,or an INSTRON Universal Material Test System) on a sample of a materialshaped as a film between about 0.003″ (76 micron) and 0.004″ (102micron) in thickness and about 1.3 cm in width, with a gauge length of5.1 cm, and a test speed of 2.5 cm/min.

Additional description of suitable primary and secondary coatings can befound in PCT Publication WO2005/010589 which is incorporated herein byreference in its entirety.

Preferably, the optical fibers disclosed herein have a low OH content,and preferably have an attenuation curve which exhibits a relativelylow, or no, water peak in a particular wavelength region, especially inthe E-band. The optical fiber disclosed herein preferably has an opticalattenuation (spectral) at 1383 nm which is not more than 0.10 dB/kmabove an optical attenuation at 1310 nm, and more preferably not morethan the optical attenuation at 1310 nm. The optical fiber disclosedherein preferably has a maximum hydrogen induced attenuation change ofless than 0.03 dB/km at 1383 nm after being subjected to a hydrogenatmosphere, for example 0.01 atm partial pressure hydrogen for at least144 hours.

A low water peak generally provides lower attenuation losses,particularly for transmission signals between about 1340 nm and about1470 nm. Furthermore, a low water peak also affords improved pumpefficiency of a pump light emitting device which is optically coupled tothe optical fiber, such as a Raman pump or Raman amplifier which mayoperate at one or more pump wavelengths. Preferably, a Raman amplifierpumps at one or more wavelengths which are about 100 nm lower than anydesired operating wavelength or wavelength region. For example, anoptical fiber carrying an operating signal at wavelength of around 1550nm may be pumped with a Raman amplifier at a pump wavelength of around1450 nm. Thus, the lower fiber attenuation in the wavelength region fromabout 1400 nm to about 1500 nm would tend to decrease the pumpattenuation and increase the pump efficiency, e.g. gain per mW of pumppower, especially for pump wavelengths around 1400 nm.

The fibers disclosed herein exhibit low PMD values particularly whenfabricated with OVD processes. Spinning of the optical fiber may alsolower PMD values for the fiber disclosed herein.

It is to be understood that the foregoing description is exemplary onlyand is intended to provide an overview for the understanding of thenature and character of the fibers which are defined by the claims. Theaccompanying drawings are included to provide a further understanding ofthe embodiments and are incorporated and constitute part of thisspecification. The drawings illustrate various features and embodimentswhich, together with their description, serve to explain the principalsand operation. It will become apparent to those skilled in the art thatvarious modifications to the embodiments as described herein can be madewithout departing from the spirit or scope of the appended claims.

What is claimed is:
 1. A single mode optical fiber comprising: (I) acore having outer radius r₁, a maximum refractive index delta percentΔ_(1max) and core alpha>5; (II) a cladding surrounding the core, thecladding comprising (i) inner cladding region having outer radius r₂ andrefractive index delta percent Δ₂, wherein Δ_(1max)>Δ₂; and (ii) atrench region surrounding the inner cladding region, the trench regionhaving an outer radius r₃>10 microns and refractive index delta percentΔ₃; and (iii) an outer cladding region having chlorine concentrationlarger than 1.2 wt. % surrounding the trench region and comprisingrefractive index delta percent Δ₄; wherein Δ_(1max)>Δ₄ and Δ₂>Δ₃, andΔ₄>Δ₃ and wherein the Δ₄−Δ₃≧0.12 percent, and said fiber exhibits a modefield diameter MFD>9 microns at 1310 nm wavelength, cable cutoff of lessthan 1260 nm, and bend loss at 1550 nm for a 15 mm diameter mandrel ofless than 0.5 dB/turn, and 1300 nm≦λ₀≦1324 nm, where λ₀ is the zerodispersion wavelength.
 2. The optical fiber of claim 1, wherein theprofile volume, ↑V₃| of the trench region is at least 30% Δmicron². 3.The optical fiber of claim 2, wherein the profile volume, |V₃| of thetrench region is at least 45% Δmicron².
 4. The optical fiber of claim 1,wherein Δ₄−Δ₃≧0.15 percent.
 5. The optical fiber of claim 1, whereinΔ_(1max)−Δ₂≧0.25 percent, and Δ_(1max)−Δ₃≧0.35; and Δ₂−Δ₃≧0.08 percent.6. The optical fiber of claim 5, wherein 0.15%≦Δ₄−Δ₃≦0.4% delta.
 7. Theoptical fiber of claim 1, wherein the core has less than 10 wt. %germania.
 8. The optical fiber of claim 1, wherein the maximum germaniaconcentration in the core region, [GeO2]_(core-max), in weight percentis 4 wt. %≦[GeO2]_(core-max)≦13 wt. %.
 9. The optical fiber of claim 1,wherein the maximum germania concentration in the core region,[GeO2]_(core-max), in weight percent is 6 wt. %≦[GeO2]_(core-max)≦12 wt.%.
 10. The optical fiber of claim 1, wherein the maximum germaniaconcentration in the core region, [GeO2]_(core-max), in weight percentis 7 wt. %≦[GeO2]_(core-max)≦11 wt. %.
 11. The optical fiber of claim 1,wherein the maximum chlorine concentration in the core region,[Cl]_(core-max), in weight percent is 1 wt. %≦[Cl]_(core-max)≦7 wt. %.12. The optical fiber of claim 1, wherein the maximum chlorineconcentration in the core region, [Cl]_(core-max), in weight percent is1 wt. %≦[Cl]_(core-max)≦6 wt. %.
 13. The optical fiber of claim 1,wherein the maximum chlorine concentration in the core region,[Cl]_(core-max), in weight percent is 1.5 wt. %≦[Cl]_(core-max)≦6 wt. %.14. The optical fiber of claim 1, wherein the trench region contains 0to 2 wt. % fluorine.
 15. The optical fiber of claim 1, wherein the outercladding region comprises Cl concentration≧1.5 weight percent.
 16. Theoptical fiber of claim 1, wherein the ratio of core radius to the innercladding radius, 1.2<r₂/r₁≦2.5.
 17. The optical fiber of claim 1, saidfiber further exhibiting a wire mesh covered drum microbend loss at 1550nm which is less than or equal to 0.05 dB/km.
 18. The optical fiber ofclaim 1, said fiber further exhibiting a wire mesh covered drummicrobend loss at 1550 nm which is less than or equal to 0.01 dB/km. 19.The optical fiber of claim 1, wherein the trench region is essentiallyfree of fluorine and germania.
 20. The optical fiber of claim 1, whereinΔ₄≧Δ₂ for a radial position extending from r₃ to a radius of at least 30microns.
 21. The fiber of claim 1, wherein said fiber exhibits anattenuation at 1550 nm which is less than or equal to 0.18 dB/km. 22.The fiber of claim 1, wherein said fiber exhibits an attenuation at 1310nm which is less than or equal to 0.32 dB/km.
 23. The fiber of claim 1,wherein the core alpha is greater than
 10. 24. The optical fiber ofclaim 1, wherein 9 microns <MFD at 1310 nm<9.5 microns.
 25. The opticalfiber of claim 1, said fiber further exhibiting a basketweave microbendloss at −60° C. at 1550 nm which is less than or equal to 0.05 dB/km.26. The optical fiber of claim 1, said fiber further exhibiting abasketweave microbend loss at −60° C. at 1550 nm which is less than orequal to 0.01 dB/km.
 27. The optical fiber of claim 1, said fiberfurther is coated with primary and secondary coatings, wherein the outerdiameter of the secondary coating is less than 250 microns.
 28. Theoptical fiber of claim 1, said fiber further is coated with primary andsecondary coatings, wherein the outer diameter of the secondary coatingis less than 210 microns.
 29. The optical fiber of claim 1, wherein theouter cladding region comprises a first outer cladding region withrefractive index delta percent Δ4 and chlorine concentration larger than1.2 wt. %; and a second outer cladding region surrounding the firstouter cladding region and comprising refractive index delta percent Δ5such that Δ4>Δ5, the second outer cladding region having chlorineconcentration of less than 0.5 wt. %.
 30. The optical fiber of claim 29,wherein viscosity of glass of said second outer cladding region isgreater than the viscosity of glass of said first outer cladding region.